Method and apparatus for transmitting/receiving data in wireless sensor network

ABSTRACT

A method and apparatus for transmitting/receiving data in a Wireless Sensor Network (WSN). The method typically includes the steps of: ascertaining characteristics of data whose transfer is requested; ascertaining a Link Quality Indication Value (LQIV); determining a level of a link state in consideration of the characteristics of the data and the LQIV; and controlling the link transfer of the data in consideration of the level of the link state. The apparatus includes a module for transmitting/receiving data in the network layer thereof having a link level determination unit for predefining a level of a link state, depending on characteristics of data and a Link Quality Indication Value (LQIV) to store a predefined level of the link state, and to determine a level of the link state. A link control unit controls the link transfer of the data in consideration of the determined level of the link state.

CLAIM OF PRIORITY

This application claims the benefit of priority under 35 U.S.C. §119(a)from an application entitled “Method and Apparatus forTransmitting/Receiving Data in Wireless Sensor Network,” filed in theKorean Intellectual Property Office on Jul. 25, 2007 and assigned SerialNo. 2007-74749, the contents of which are incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Wireless Sensor Network (WSN). Moreparticularly, the present invention relates to the technology oftransmitting/receiving data in a WSN and problems associated withunstable wireless links. Still more particularly, the present inventionrelates to a Wireless Sensor Network (WSN), and specifically to a methodfor checking wireless channel connection states and a type of data to betransmitted among devices constructing a WSN, and then controlling datatransfer in consideration of the result of the check.

2. Description of the Related Art

A WSN differs from existing networks that have been realized forcommunication in that the WSN has been embodied for the purpose ofcollecting remote information. The WSN is typically equipped with asensor node for processing information collected via a sensor and thentransferring the processed information, and a sink node for sendingtransferred information to the outside. As a network is constructed of alarge number of sensor nodes constructs a network, the structure of eachsensor node should be simply designed. Also, since a certain sensor nodemay be arranged in an area to which it is difficult for a person to getaccess, the sensor nodes should be designed to consume little electricpower so that the sensor node may operate for up to several months orseveral years with the same battery. In addition, the sensor nodes mustbe designed to have mobility so that each position in which the sensornode has been installed is enabled to be freely moved. Furthermore, eventhough some sensor nodes existing within the network are subject tobeing damaged, the WSN must be embodied so as not to be affected by themaintenance of the network.

Meanwhile, IEEE 802.15 Working Group defines the standards for ashort-distance wireless network. More particularly, since the IEEE802.15.4 standard defined by IEEE 802.15 Working Group enables low powershort-distance wireless network to be realized, the IEEE 802.15.4standard is quickly becoming a core technology which is suitable forbeing applied to a sensor network.

The IEEE 802.15.4 standard defines communication protocol related to thephysical layer and the Medium Access Control Layer (hereinafter,referred to as the “MAC Layer”) within a short-distance wirelessnetwork. Furthermore, the IEEE 802.15.4 standard discloses data frametransfer between a transmission apparatus and a receiving apparatus. Indata frame transfer between a transmission apparatus and a receivingapparatus, the IEEE 802.15.4 provides a transfer process inconsideration of three cases, FIGS. 1A to 1C illustrate a transferprocess relevant to each case. Hereinafter, with reference to FIGS. 1Ato 1C, a description will be made in detail of a transfer processrelevant to each case.

(1) In the Case of Successful Transfer of a Data Frame and anAcknowledgement (ACK) frame:

With reference to FIG. 1A, a transmission apparatus MAC layer 12 isrequested to transmit a data frame from a transmission apparatus networklayer 11 (step S100), and requests a transmission apparatus physicallayer 13 to transmit a data frame (step S110). Then, the transmissionapparatus physical layer 13 transmits a data frame to a receivingapparatus 2023 (step S120), and informs the transmission apparatus MAClayer 12 that the data frame has been transmitted (step S130).Accordingly, the transmission apparatus MAC layer 12 enables a timer tooperate, and waits for receiving an ACK frame for a prescribed timeinterval, e.g., a period of time during which receiving the ACK framefrom a receiving apparatus 20 is expected (step S140).

Meanwhile, if a receiving apparatus physical layer 23 receives the dataframe, the receiving apparatus physical layer 23 informs a receivingapparatus MAC layer 22 that the data frame has been received (stepS200). Then, the receiving apparatus MAC layer 22 delivers the receiveddata frame to a receiving apparatus network layer 21 (step S210), andrequests the receiving apparatus physical layer 23 to transmit the ACKframe to the transmission apparatus MAC layer 12 (step S220). Inaddition, the receiving apparatus physical layer 23 transmits the ACKframe to a transmission apparatus physical layer 10 (step S230), andinforms the receiving apparatus MAC layer 22 that the ACK frame has beenreceived (step S240).

Still referring to FIG. 1A, the transmission apparatus physical layer 13delivers the ACK frame received from the receiving apparatus physicallayer 23 to the transmission apparatus MAC layer 12 (step 5300). Thetransmission apparatus MAC layer 12 enables a timer to be terminated,and informs the transmission apparatus network layer 11 that thetransfer of the data frame has been completed (step S310).

(2) In the case of unsuccessful transfer of a data frame:

With reference to FIG. 1B, in the case of unsuccessful transfer of adata frame, by performing steps S100 to S140 as in the above-describedcase (i.e., in the case of successful transfer of a data frame), a datatransfer is requested, and waiting for the reception of an ACK frame isimplemented.

However, a wireless link state is often unstable between thetransmission apparatus and the receiving apparatus, and therefore, adata frame transmitted from the transmission apparatus physical layer 13cannot be delivered up to the receiving apparatus physical layer 23.Accordingly, the transmission apparatus physical layer 13 cannot receivethe ACK frame from the receiving apparatus 20. After all, thetransmission apparatus MAC layer 12 fails to receive the ACK frame untila timer is terminated, and repeatedly performs steps S110 to S140.

The transmission apparatus MAC layer 12 repeats this process up to threetimes, and if the transmission apparatus MAC layer 12 cannot receive aspecial ACK frame, it does not attempt to transmit the data frame againfor a fourth time, but informs the transmission apparatus network layer11 that the transfer of the data frame has failed (step S350).

(3) In a case where the transfer of a data frame has been successful butthe transfer of an ACK frame fails:

With reference to FIG. 1C, in a case where the transfer of an ACK framehas failed, as in the above-described case (i.e., in the case ofsuccessful transfer of a data frame), the transmission apparatus 10performs steps S100 to S140 to request data transfer, and waits forreceiving an ACK frame. In addition, the receiving apparatus 20 deliversa data frame received through steps S200 to S240, to the receivingapparatus network layer 21, and transmits the ACK frame to thetransmission apparatus 10.

However, since a wireless link state between the transmission apparatusand the receiving apparatus is unstable, the ACK frame transmitted fromthe receiving apparatus physical layer 23 cannot be delivered up to thetransmission apparatus 10.

Finally, the transmission apparatus MAC layer 12 fails to receive theACK frame until the timer is terminated, and repeatedly performs stepsS110 to S140. The transmission apparatus MAC layer 12 repeats thisprocess up to three times, and if the transmission apparatus MAC layer12 cannot receive a special ACK frame, it does not attempt to transmitthe data frame for a fourth time, but finally informs the transmissionapparatus network layer 11 that the transfer of the data frame hasfailed (step S350).

Furthermore, Zigbee Union has tried the standardization of protocols ofupper layers (the network layer and an application layer) which have notbeen suggested in the Zigbee protocol based on the IEEE 802.15.4standard, i.e. the IEEE 802.15.4 standard. However, even in the Zigbeeprotocol, any plan for overcoming the above problem (i.e., a problemthat the transfer of data is not implemented due to coupling errorsamong nodes) raised in the IEEE 802.15.4 standard has not beenconsidered, either, and a solution to the above problem has not beensuggested.

In order to embody a WSN, the reliability of each data frame transmittedamong nodes must be secured. However, when the WSN is realized based ona protocol suggested in the IEEE 802.15.4 standard, or the Zigbeeprotocol, a wireless link state between specific nodes is unstable, andthen, an error in data transfer can be caused repeatedly. Namely, aproblem that the reliability of a data frame transmitted throughunstable wireless link is raised. However, despite the occurrence ofthis problem, data has been transmitted uniformly by applying the sameconditions without considering a state of each wireless link at all.Hence, there is a need in the art to solve at least the above-identifiedproblems in the art.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made in part to solve atleast some of the above-stated problems occurring in the prior art, andto provide some of the advantages described herein below. The presentinvention provides a method in which the reliability of data transfercan be guaranteed in consideration of a state of a wireless link in aWSN.

In order to accomplish this exemplary aspect of the present invention,there is provided a method for transmitting/receiving data in a WirelessSensor Network (WSN), including the steps of: (a) ascertainingcharacteristics of data whose transfer is requested; (b) ascertaining aLink Quality Indication Value (LQIV); (c) determining a level of a linkstate in consideration of the characteristics of the data and the LQIV;and (d) controlling the link transfer of the data in consideration ofthe level of the link state.

Preferably, in step (c), the ascertained characteristics of data andLQIV are applied to, for example, a predetermined value, and a levelcorresponding to the result of the application is determined.

Preferably, in step (d), the number of times of data re-transfer, alength of a waiting time interval for a response of data transfer, andthe number of data frames to be transmitted by duplicating original datacan be controlled in consideration of the level of the link statedetermined in step (c).

More preferably, in step (a), characteristics of data are ascertainedwhose transfer is requested by an upper layer.

Also, step (b) includes the steps of: (b1) ascertaining an LQIV in aphysical layer; and (b2) delivering the ascertained LQIV to a networklayer.

More preferably, step (b1) is performed by request of the network layerrequested to transmit data. Also, in steps (b1) and (b2), performingsteps (b1) and (b2) is implemented in an initialization process of anetwork, the network layer temporarily stores the LQIV received from thephysical layer, and the stored LQIV is checked as occasion demands.

Preferably, steps (c) and (d) are performed in the network layer.

In accordance with another exemplary aspect of the present invention,there is provided a module for transmitting/receiving data in a WirelessSensor Network (WSN), including: a link level determination unit forpredefining a level of a link state, depending on characteristics ofdata and a Link Quality Indication Value (LQIV), for ascertainingcharacteristics of data and an LQIV received from a lower layer, and fordetermining a level of a link state by applying the receivedcharacteristics of data and LQIV to the predefined level of the linkstate; and a link control unit for controlling the link transfer of thedata in consideration of the determined level of the link state.

Preferably, the link level determination unit stores the number of timesof data re-transfer equivalent to the predefined level of the linkstate, and the link control unit controls the number of times of datare-transfer by applying the determined level of the link state to thepredefined level of the link state.

Preferably, the link level determination unit stores a length of awaiting time interval for data transfer equivalent to the predefinedlevel of the link state, and the link control unit controls a length ofa waiting time interval for data transfer by applying the determinedlevel of the link state to the predefined level of the link state.

Preferably, the link level determination unit stores the number of dataframes to be transmitted by duplicating original data, depending on thepredefined level of the link state, and the link control unit controlsthe number of data frames to be transmitted by duplicating original datawith the application of the determined level of the link state to thepredefined level of the link state.

Preferably, the link level determination unit and the link control unitare provided to a network layer.

In addition, the link level determination unit checks a type of datareceived from an upper layer.

In addition, the link level determination unit receives an LQIV from aphysical layer, and then checks a magnitude of the received LQIV.

More preferably, the link level determination unit is requested totransmit data by an upper layer, and then requests the physical layer toprovide the LQIV in real-time, or the link level determination unitrequests the LQIV in an initialization process of a network, temporarilystores the LQIV, and then checks the stored LQIV as occasion demands.

In accordance with a further exemplary aspect of the present invention,there is provided an apparatus for transmitting/receiving data, having aphysical layer, a Medium Access Control (MAC) Layer, and a network layerin a Wireless Sensor Network (WSN). The apparatus includes: a module fortransmitting and receiving data in the network layer thereof, the moduleincluding: a link level determination unit for predefining a level of alink state, depending on characteristics of data and a Link QualityIndication Value (LQIV) to store the predefined level of the link state,and for determining a level of a link state by applying characteristicsof data and an LQIV received from the physical layer to the predefinedlevel of the link state; and a link control unit for controlling thelink transfer of the data in consideration of the determined level ofthe link state. The ascertained characteristics may include a type ofdata which indicates that data belonging to a data frame delivered by ahigh layer or lower layer corresponds to, for example, event-drivendata, periodic data, or the rest.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other exemplary features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1A to 1C are flowcharts illustrating procedures of methods fortransmitting data according to the prior art, respectively;

FIG. 2 is a conceptual view illustrating the network structure of a WSNbased on the IEEE 802.15.4 standard protocol according to an exemplaryembodiment of the present invention;

FIG. 3 is a conceptual view illustrating the structure of a stack of anapparatus for transmitting/receiving data provided to a WSN according toan exemplary embodiment of the present invention;

FIG. 4 is a flowchart illustrating the procedure of a data transferprocess of a method for transmitting/receiving data according to anexemplary embodiment of the present invention;

FIG. 5 is a flowchart illustrating the procedure of a data receiveprocess of a method for transmitting/receiving data according to anexemplary embodiment of the present invention;

FIG. 6 is a flowchart illustrating a procedure for processing data onreceiving an ACK in a method for transmitting/receiving data accordingto an exemplary embodiment of the present invention;

FIG. 7 is a flowchart illustrating a procedure for processing data,responding to a case where an ACK is not received in a method fortransmitting/receiving data according to an exemplary embodiment of thepresent invention; and

FIG. 8 is a graph illustrating the test results of a method fortransmitting/receiving data according to an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Thenext description includes particulars, such as specific configurationelements, which are only provided to facilitate more comprehensiveunderstanding of the present invention, and it will be obvious to thoseof ordinary skill in the art that prescribed changes in form andmodifications may be made to the particulars in the scope of the presentinvention. For the purposes of clarity and simplicity, a detaileddescription of known functions and configurations incorporated herein isomitted as it may make appreciation of the subject matter of the presentinvention unclear to a person of ordinary skill in the art.

An exemplary embodiment of the present invention corresponds to arepresentative example of a WSN, and exemplifies a WSN based on the IEEE802.15.4 standard protocol.

First, in accordance with FIG. 2, in order to examine the networkstructure of the WSN based on the IEEE 802.15.4 standard protocolaccording to an exemplary embodiment of the present invention, the WSNaccording to is the example shown and described is typically constructedin a network structure having a multi cluster form in which a startopology and a peer-to-peer topology are combined. Specifically, the WSNaccording to this exemplary embodiment includes: a first cluster CID1realized with a Personal Area Network (PAN) coordinator as the center; asecond cluster CID2 which includes a first cluster hub CLH1 linked to adevice included in the first cluster CID1, and is realized with thefirst cluster hub CLH1 as the center; a third cluster CID3 whichincludes a second cluster hub CLH2 linked to a device included in thesecond cluster CID2, and is realized with the second cluster hub CLH2 asthe center; and a fourth cluster CID4 which includes a third cluster hubCLH3 linked to the second cluster CID2, and is realized with the thirdcluster hub CLH3 as the center.

Still referring to FIG. 2, the above multi-cluster is formed with thePAN coordinator as the center. In the first place, if the PANcoordinator forms the first cluster CID1 by performing functions,including network settings, beacon transfer, node management, nodeinformation storage, and message route setting between connected nodes,devices included in the first cluster CID1 scan a specified channel listso as to check a usable communication channel. Then, if a WirelessPersonal Area Network (WPAN) IDentification (ID) which is not duplicateis selected following the completion of scanning, a Full Function Device(FFD) which can directly transmit/receive data functions as the firstcluster hub CLH1. Thereafter, if the first cluster hub CLH1 transmits abeacon frame to other devices, the devices all of which receive thebeacon frame are linked to the first cluster hub CLH1, and then form thesecond cluster CID2. By repeating the aforementioned process, the thirdand the fourth clusters CID3 and CID4 are embodied, and finally, one WSNis formed.

FIG. 3 corresponds to a view according to an exemplary embodiment of thepresent invention, and illustrates the structure of a stack of anapparatus for transmitting/receiving data provided to the WSN. Nowreferring to FIG. 3, the exemplary apparatus for transmitting/receivingdata includes a PHYsical (PHY) layer 100, a Medium Access Control (MAC)layer 200, a network layer 300, and an upper layer 400. The physicallayer 100 corresponds to an interface that connects the MAC layer 200with a wireless channel, and provides a PHY data service thattransmits/receives a data frame, and a PHY management service that setsa communication environment of a wireless domain. As the PHY dataservice, the physical layer 100 is requested to transmit a data frame bythe MAC layer 200, and then transmits a packet of the PHY layer, i.e. aPHY Protocol Data Unit (PPDU), to a receiving apparatus via a wirelesschannel. Then, the PHY layer 100 delivers a confirmation message inregard to the transfer of the data frame to the MAC layer 200. Also, thePHY layer 100 receives a transfer ACKnowledgement (ACK) frame from thereceiving apparatus, and then informs the MAC layer 200 that the datahas been successfully transmitted. Additionally, as the PHY managementservice, the PHY layer 100 performs activation or deactivation of awireless domain requested by the MAC layer 200, performs Channel ClearAssignment (CCA), detects energy of the wireless channel, and checks alink state of the wireless channel. Furthermore, the PHY layer 100 isconnected with the wireless channel via a Radio Frequency-Service AccessPoint (RF-SAP), and is connected with the MAC layer 200 via a PHYData-Service Access Point (PD-SAP) and a PHY Layer ManagementEntity-Service Access Point (PLME-SAP).

Still referring to FIG. 3, the MAC layer 200 corresponds to an interfacethat connects the PHY layer 100 with the network layer 300, and providesan MAC data service that transmits/receives an MAC data frame, and anMAC management service that sets a communication environment. As the MACdata service, the MAC layer 200 is requested to transmit a data frame(e.g., a Network Service Data Unit (NSDU)) by a higher layer, i.e. thenetwork layer 300, generates data of the MAC layer (i.e., an MACProtocol Data Unit (MPDU)), and then delivers the generated MPDU to thePHY layer 100. Then, the MAC layer 200 provides the network layer 300with a confirmation message in regard to the transfer of the data frameand the result in regard to the transfer of the data frame that the PHYlayer 100 has reported to the MAC layer 200. As the MAC managementservice, the MAC layer 200 sets an environment in which it is suitablefor the PHY layer 100 to transmit a data frame to each of neighbornodes. On this end, the MAC layer 200 transmits the control valuenecessary to set an environment to the PHY layer 100, and then receivesa response accompanied by the control result. Specifically, the MAClayer 200 generates a beacon, and also produces a control signalnecessary to synchronize the generated beacon. Thereafter, the MAC layer200 controls an association and disassociation of a WPAN, and then setsan environment in which a Carrier Sense Multiple Access/CollisionAvoidance (CSMA/CA) mechanism and a Global Telecommunication System(GTS) mechanism can be performed. Furthermore, the MAC layer 200 isconnected with the network layer 300 (i.e., a higher layer) via an MACCommon Part Sublayer-Service Access Point (MCPS-SAP), and is connectedwith the PHY layer 100 (i.e., a lower layer) via a PHY Data ServiceAccess Point (PD-SAP), thereby performing the MAC data service. Inaddition, the MAC layer 200 is connected with the network layer 300(i.e., a high layer) via an MAC Layer Management Entity-Service AccessPoint (MLME-SAP), and is connected with the PHY layer 100 (i.e., a lowerlayer) via a PHY Layer Management Entity-Service Access Point(PLME-SAP), thereby performing the MAC management service.

The network layer 300 provides a network data service thattransmits/receives a data frame, and a network management service thatsets a communication environment. The network data service generates adata frame of the network layer (i.e., a Network Packet Data Unit(NPDU)) by using a data frame delivered from a higher layer, and thendelivers the generated NPDU to the MAC layer 200. The network managementservice provides the function of generating the control value necessaryto find routes of a receiving-end and then set a route thereof.

In addition, the network management service generates the control valuenecessary to manage a transmit/receive apparatus which attempts to entera network, or a transmit/receive apparatus which tries to leave thenetwork. Also, when a transmit/receive apparatus functions as a clusterhub, the network data service performs the function for assigning theaddress values of transmit/receive apparatuses existing within thenetwork.

In particular, the network layer 300 is equipped with a data transfermodule including a link level determination unit and a link controlunit. The link level determination unit requests the MAC layer 200 toprovide a Link Quality Indication Value (LQIV), and then receives theLQIV. Then, the network layer 300 checks a type of data which indicatesthat data belonging to a data frame delivered by a higher layer or alower layer corresponds either to event-driven data, to periodic data,or to the rest. Additionally, in consideration of the results (i.e., theLQIV and the type of data), the network layer 300 determines a linklevel corresponding to those results. The link control unit considersthe link level determined by the link level determination unit, and thengenerates the control value corresponding to the determined link level.

Herein, the above control value can include the value necessary to setwaiting time for which the MAC layer 200 waits until the reception of aresponse.

When a link state is unstable, the time required until the reception ofan ACK frame can increase. Thus, if a prescribed waiting time isarbitrarily set without regard to a link state, because the waiting timeis too short, the ACK frame can be received after the expiration of thewaiting time, and a situation can occur in which unnecessary data isretransmitted even though the ACK frame has been received. In contrast,if the link state is stable, following the transfer of a data frame, theACK frame can be received within a short amount of time. However, if aprescribed waiting time is arbitrarily set without regard to the linkstate, a situation can occur in which the MAC layer 200 waits for anunnecessary until the expiration of the waiting time interval eventhough the ACK frame has already been received. Hence, if the waitingtime is controlled in consideration of the LQIV and a type of data, boththe transfer of unnecessary data and the transfer delay caused byunnecessary waiting time can be prevented. With this control, it iseffective in that electric power required for data transmit/receive canbe reduced.

Further, the above control value can include the value necessary tocontrol the number of times for data re-transfer. Also, the abovecontrol value can include the value necessary to control the number ofdata frames to be transmitted by duplicating original data during datatransfer. If a link state is unstable, the probability of failure indata transfer is relatively higher when compared with the case of astable link state. Therefore, if the number of times of data re-transferand the number of data frames to be transmitted with the duplication oforiginal data increases, relatively stable data transfer can beimplemented as compared with a case where a predetermined number oftimes of data re-transfer and a predetermined number of data frames tobe transmitted with the duplication of original data are arbitrarilydefined without regard to a link state.

Hereinafter, a description will be made in detail of a method fortransmitting data according to an exemplary embodiment of the presentinvention. Above all, so that each device may transmits/receives data,each device must be connected and synchronized with one another via awireless channel, and a WSN must be formed by assigning an addressthereof to each device. In an exemplary embodiment of the presentinvention, it is assumed that the WSN is formed by a method proposed inthe IEEE 802.15.4 protocol or the Zigbee protocol. Also, it isexemplified that the WSN includes an exemplary apparatus fortransmitting/receiving data, capable of routing, (e.g., a coordinator ora router), and each of those devices (e.g., nodes having thecapabilities of routing) stores a route table in which relations withperipheral devices are stored.

FIG. 4 is a flowchart illustrating an exemplary data transferringprocess for an apparatus for transmitting/receiving data according to anembodiment of the present invention. FIG. 5 is a flowchart illustratingan exemplary data receiving process of an apparatus fortransmitting/receiving data according to the present invention. FIG. 6is a flowchart illustrating an exemplary procedure for processing dataon receiving an ACK in an apparatus for transmitting/receiving data.FIG. 7 is a flowchart illustrating an exemplary procedure for processingdata, responding to a case where an ACK is not received in an apparatusfor transmitting/receiving data.

First, in a state in which a network is formed, if a network layer ofthe apparatus for transmitting/receiving data which acts as atransmission apparatus is requested to transmit a data frame (i.e., aNext Higher layer Protocol Data Unit (HPDU)) by an upper network (stepS10), it sets a transfer route (step S11).

In more detail, in step S11 if a route to a destination is not definedin a route table possessed by a current transmission apparatus, thenetwork layer transmits a route request instruction frame to a neighbordevice until it find out a device which knows the destination or a routeto the destination. Then, a device which has received the route requestinstruction frame checks a route table possessed by the device itself,and then ascertains if a request route is defined in the route tablethereof. Thereafter, the device generates an instruction framerepresenting a route reply, and then transmits the generated instructionframe back to a device which has requested route search. Further, ifmultiple routes exist as the route to the destination, the device whichhas received the route request instruction frame computes link costsamong devices, and then selects a route whose cost is the lowest. Inaddition, a newly made entry in regard to the route set as above isstored in a route search table of each of all devices from a deviceinitiating route search to a final reply device, which exists within theroute.

While a method for finding a transfer route to a destination by using adevice which stores a route table is exemplified as a method for settinga transfer route in an embodiment of the present invention, the presentinvention is not limited to this, and it goes without saying thatvarious routing methods used in communication protocols can be appliedto exemplary embodiments of the present invention. For example, as amethod for setting a transfer route, a hierarchical routing method canbe used. Namely, after a network layer of a transmission apparatuschecks a destination address included in a data frame and ascertains ifa destination exists within an address part block thereof, the networklayer of the transmission apparatus delivers the address to a device ofa lower layer. If that happens, the device of the lower layer repeats aprocess in which it checks again if the above address exists within anaddress part block thereof, and then delivers the address to asubordinate device. Finally, a route to the destination can also beformed.

Also, so as to exemplify a method for setting a transfer route by usinga route table in an exemplary embodiment of the present invention, whileit is exemplified that a WSN typically includes devices having thecapability of routing (e.g., a coordinator or a router), and each ofthose devices (i.e., the devices capable of routing) stores a routetable in which relations with peripheral devices are stored, the presentinvention is not limited to this method operation. A person of ordinaryskill in the art can appreciate that the spirit of the invention andscope of the appended claims includes methods for setting a transferroute, a WSN and configuration elements included therein can be replacedwith other configuration elements in addition to the examples of what isshown and described herein.

In step S12, a data frame (e.g., HPDU) delivered from the upper layer ischecked, and then a type of a data unit (e.g., a next Higher layerService Data Unit (HSDU)) included in the HPDU is confirmed. Forinstance, if the upper layer defines a type of data of the HPDU and thendelivers the HPDU to the network layer, the network layer checks a frameformat of the HPDU, and then confirms a type of the HSDU. At this time,the upper layer directly defines a type of data in the frame format ofthe HPDU and then transmits the HPDU, or checks a type defined in aframe format and can then ascertain a kind corresponding to the definedtype. For example, the above data type can correspond to either‘event-driven’, ‘on-demand’, ‘periodic’, or the rest.

In step S13, a link state of a wireless channel of the route which hasbeen set is checked. For example, in an initialization process of anetwork, the PHY layer measures the LQIV, and then delivers the resultof the measurement to the MAC layer. Accordingly, it is preferable thatthe network layer receives the LQIV from the MAC layer to temporarilystore the received LQIV, and as occasion demands, confirms the LQIVselectively, i.e. in a process for performing step S13.

Although in the example shown and described the LQIV measured in aninitialization process is temporarily stored and then selectivelyconfirms the above LQIV as a method for checking an LQIV, the presentinvention is not limited to measurement of the LQIV as shown anddescribed. For instance, it is also possible that, in step S13, the MAClayer is requested to measure an LQIV in real time as occasion arises,and then confirms the LQIV received in reply to the request of themeasurement. If the type of the HSDU and the LQIV are confirmed throughsteps S12 and 513, the network layer applies the confirmed type of theHSDU and the LQIV to a predetermined value, and then sets a link levelreflected in a the transfer of a data frame (step S14). Additionally,the predetermined value can be determined as exemplified in TABLE 1. TheLQIV can be an integer between 0 to 255. Also, in the table 1 the lowLQI value can be an integer between 0 to 100, the medium LQI value canbe an integer between 101 to 200, and the high LQI value can be aninteger between 201 to 255. Although in the example the LQVI is integerbetween 0 to 255 and the low LQI value, the medium LQI value, and thehigh LQI value is integer within a above mentioned range respectively,the present invention is not limited to the LQVI. It is also possiblethat the LQVI can be modified multifariously according to a networkenvironment, a power of a network device, or application program.

For example, if the type of the HSDU confirmed in step S12 correspondsto ‘on-demand’ (i.e., an ACK frame), and if the LQIV confirmed in stepS13 has a low-level value (i.e., a low Link Quality Indication (LQI)),in step S14, the third link level can be determined as a link level.

TABLE 1 ADAPTIVE LINK TABLE application LQI value feature high LQImedium LQI low LQI event-driven link level 2 link level 3 link level 3on-demand link level 2 link level 2 link level 3 Periodic link level 1link level 2 link level 3

In step 515, corresponding to the link level determined in step S14, acontrol value necessary to transmit a data frame is determined, andthen, the determined control value is delivered to the MAC layer.

Preferably with regard to the control value determined in step S15,there includes waiting time, and the number of times of re-transfer, aswell as the number of data frames to be transmitted with duplication;more particularly, the control values may correspond to either any one,or two or more units of waiting time, the number of times ofre-transfer, and the number of data frames to be transmitted withduplication.

Specifically, in step S15, the link level determined in step S14 isapplied to a predetermined value exemplified in TABLE 2, and then, acontrol value (e.g., a predetermined waiting time, the number of timesof re-transfer, and the number of data frames to be transmitted withduplication) corresponding to the determined link level can bedetermined. Namely, if the link level determined in step S14 correspondsto a level which indicates that a link state is unstable (i.e., MDR L3),in step S15, the waiting time is set to ‘120’, the number of times ofre-transfer is set to ‘five times’, and the number of data frames to betransmitted with duplication can be set to ‘2.’

TABLE 2 ADAPTIVE TRANSMISSION TABLE wait duration retries Action MDR L1 27 2 None MDR L2  54 3 none (802.15.4) (802.15.4) (802.15.4) MDR L3 1205 two copies

Next, the network layer transmits, to the MAC layer, a data frame (e.g.,an NPDU) including the control value set in step 155, and then requeststhe MAC layer to transmit the data frame to the receiving apparatus(step S16). If that happens, the MAC layer checks a state of the PHYlayer, and then confirms an availability state of a channel connectedwith the receiving apparatus (step S20). Step S20 can include a processin which the MAC layer controls an operation mode (e.g., a transmitmode, a receive mode, etc.) of the PHY layer, and a process in which theMAC layer requests the PHY layer to provide Channel Clear Assignment(CCA).

Still referring to FIG. 4, following step S20, the MAC layer delivers adata frame (e.g., an MPDU) to the PHY layer, and then requests the PHYlayer to transmit the data frame to the receiving apparatus (step S21).Then, the PHY layer generates a data frame (i.e., a PPDU), including thedata frame delivered as above and a PHY header, to transmit thegenerated PPDU to the receiving apparatus (step S30), and informs theMAC layer that the data frame (the PPDU) has been transmitted.

The MAC layer which has confirmed the transfer of the data frame (thePPDU) on the basis of the above notice from the PHY layer, refers to thewaiting time included in the control value received in step S16, andthen waits for a reply generated from the receiving apparatus during atime interval equivalent to the waiting time.

Meanwhile, FIG. 5 is a flowchart illustrating a process in which areceiving apparatus according to another exemplary embodiment of thepresent invention receives data. Hereinafter, the data receive processaccording to an embodiment of the present invention will be examinedwith reference to FIG. 5.

First, a PHY layer of the receiving apparatus receives the data frame(i.e., the PPDU) from the transmission apparatus (step S40), and checksthe received data frame to deliver an MPDU to an MAC layer of thereceiving apparatus (step S41). If that happens, the MAC layer confirmsthe MPDU to deliver an NPDU to a network layer again (step S50), andrequests the PHY layer to transmit an ACK frame (step S51). Also, thenetwork layer to which the NPDU has been delivered by the MAC layer,checks the above data frame (the NPDU), and then delivers an HPDU to anupper layer (step S60). In the meantime, the PHY layer which has beenrequested to transmit the ACK frame, transmits the ACK frame to thetransmission apparatus (step S42), and then informs the MAC layer thatthe ACK frame has been transmitted (step S43).

If a connection state of a wireless channel between the transmissionapparatus and the receiving apparatus is stable, as illustrated in FIGS.4 and 5, data transmitted from the transmission apparatus is deliveredto the receiving apparatus, and the ACK frame transmitted from thereceiving apparatus can be delivered to the transmission apparatus. Onthe contrary, if a connection state of a wireless channel between thetransmission apparatus and the receiving apparatus is unstable, a dataframe transmitted from the transmission apparatus is not delivered tothe receiving apparatus. Alternatively, even when the data frame isdelivered to the receiving apparatus, the ACK frame may not be deliveredto the transmission apparatus.

FIG. 6 is a flowchart illustrating a process in which a transmissionapparatus according to an exemplary embodiment of the present inventionprocesses data in response to the reception of an ACK frame. FIG. 7 is aflowchart illustrating a process in which a transmission apparatusaccording to an exemplary embodiment of the present invention processesdata in response to a case where an ACK frame is not received. Namely,FIG. 6 depicts a state in which a connection state of a wireless channelbetween the transmission apparatus and the receiving apparatus isstable, and illustrates a process after the transmission apparatusreceives the ACK frame. FIG. 7 depicts a state in which a connectionstate of a wireless channel between the transmission apparatus and thereceiving apparatus is unstable, and illustrates an exemplary operationof a case where the transmission apparatus cannot receive the ACK frame.

In FIG. 6, the PHY layer of the transmission apparatus receives the ACKframe from the receiving apparatus (step S32), and then informs the MAClayer, which waits for a reply to transfer, that the data frame (i.e.,the MPDU) has been successfully transmitted (step S33). Then, the MAClayer informs the network layer that the data frame (i.e., the NPDU) hasbeen successfully transmitted (step S23), and the network layer informsthe upper layer again that the data frame (i.e., the HPDU) has beensuccessfully transmitted (step S17).

On the other hand, as shown in FIG. 7, if, in such a state that the MAClayer of the transmission apparatus cannot receive the ACK frame fromthe receiving apparatus, waiting time for which the MAC layer of thetransmission apparatus is expected to receive a transfer ACK expires,the MAC layer checks the number of re-transfer attempts that correspondto the control value received in step S16 (step S24). If it isdetermined as a result of performing step S24 that all of the number oftimes of re-transfer attempts directed by the above control value hasbeen tried, the MAC layer informs the network layer that the transfer ofthe data frame (i.e., the NPDU) has failed (step S25). Then, the networklayer informs the upper layer again that the transfer of the data frame(i.e., the HPDU) has failed (step S18). In the meantime, if, as a resultof performing step S24, the quantity of transfer attempts does notexceed the quantity of re-transfer attempts directed by the abovecontrol value, the MAC layer requests the PHY layer to retransmit thedata frame (i.e., the MPDU) (step S26). In such a case, the PHY layertransmits the data frame (i.e., the PPDU) to the receiving apparatus(step S34), and then informs the MAC layer again that the data frame(i.e., the PPDU) has been transmitted to the receiving apparatus (stepS35). Thereafter, the MAC layer repeats a step of waiting for a transferACK during waiting time included in the control value (step S22).

Also, in the process of repeating step S22, if the ACK frame is receivedfrom the receiving apparatus, steps S23 and S17 described in FIG. 6 areperformed, and if the ACK frame is not received for waiting time, stepS24 is performed. After that, depending on the result of step S24, stepsselected among steps S25, S26, S34, S35, and S18 are performed.

FIG. 8 is a graph illustrating the test results of a method fortransmitting/receiving data according to an exemplary embodiment of thepresent invention.

As a comparative example, FIG. 8 shows the transfer efficiency for databeing transmitted through a method for transmitting/receiving data,proposed in the IEEE 802.15.4 protocol. At this time, a transmissionerror rate is set to 0.01%, and, while the number of nodes between thetransmission apparatus and the receiving apparatus is varied from ‘3’ to‘100’, data transfer efficiency is measured for one hour. In addition,the measured data transfer efficiency is shown in a dotted line of agraph.

Meanwhile, in an exemplary embodiment of the present invention, data istransmitted through a method for transmitting/receiving data accordingconditions as described in the above comparative example, and while thenumber of nodes between a transmission apparatus and a receivingapparatus varies from ‘3’ to ‘100’, data transfer efficiency is measuredfor one hour. In addition, the measured results are shown in a solidline of a graph.

Referring to FIG. 8, it can be confirmed that transfer efficiency isrelatively and remarkably higher in the exemplary embodiment of thepresent invention when compared with the comparative example proposed inthe IEEE 802.15.4 protocol. Thus, if data is transmitted/received with asuitable link state of a wireless channel and a suitable type of data inthe method for transmitting/receiving data according to the presentinvention, the data can be stably delivered to the receiving apparatus,and the transfer efficiency can also be increased significantly.

While it is exemplified that a WSN is formed in a method proposed in theIEEE 802.15.4 protocol or the Zigbee protocol in an embodiment of thepresent invention, the present invention is not limited to this, if aWSN for data transmit/receive is embodied, that will do.

The merits and effects of exemplary embodiments, as disclosed in thepresent invention, and as so configured to operate above, will bedescribed as follows.

As described above, in a method for transmitting/receiving dataaccording to the present invention, considering link states of wirelesschannels and types of data, data can be delivered to a receivingapparatus, and data transfer efficiency can also be raised. Furthermore,an unnecessary waiting time, an unnecessary number of times ofre-transfer, and the like can be controlled in consideration of linkstates and types of data, and accordingly, electric power required indata transfer can be reduced.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention.Therefore, the spirit of the present invention and the scope of theappended claims are not limited to the exemplary embodiments thereof.

1. A method for transmitting/receiving data in a Wireless Sensor Network(WSN), the method comprising the steps of: (a) ascertainingcharacteristics of data whose transfer is requested; (b) ascertaining aLink Quality Indication Value (LQIV); (c) determining a level of a linkstate based on the characteristics of the data and the LQIV; and (d)controlling the link transfer of the data based on the level of the linkstate.
 2. The method as claimed in claim 1, wherein step (c) includesapplying the ascertained characteristics of data and LQIV to apredetermined value, and determining the level of the link statecorresponding to the result of the application.
 3. The method as claimedin claim 1, wherein, in step (d), the number of times that data transferis attempted is controlled based on the level of the link statedetermined in step (c).
 4. The method as claimed in claim 1, wherein, instep (d), a length of a waiting time interval for a response of datatransfer is controlled based on the level of the link state determinedin step (c).
 5. The method as claimed in claim 1, wherein, in step (d),the number of data frames to be transmitted is controlled by duplicatingoriginal data based on the level of the link state determined in step(c).
 6. The method as claimed in claim 1, wherein, in step (a),characteristics of data whose transfer is requested by an upper layerare ascertained.
 7. The method as claimed in claim 6, wherein step (b)comprises the steps of: (b1) ascertaining an LQIV in a physical layer;and (b2) delivering the ascertained LQIV to a network layer.
 8. Themethod as claimed in claim 7, wherein step (b1) is performed by requestof the network layer requested to transmit data.
 9. The method asclaimed in claim 7, wherein, steps (b1) and (b2) are implemented in aninitialization process of a network, the network layer temporarilystoring the LQIV received from the physical layer, and the stored LQIVis checked upon demand.
 10. The method as claimed in claim 6, whereinsteps (c) and (d) are performed in the network layer.
 11. A module fortransmitting/receiving data in a Wireless Sensor Network (WSN), themodule comprising: a link level determination unit for predefining alevel of a link state, wherein the link state depends uponcharacteristics of data and a Link Quality Indication Value (LQIV), andsaid link level determination unit for ascertaining characteristics ofdata and an LQIV received from outside the WSN, and for determining alevel of a link state by applying the received characteristics of dataand LQIV to the predefined level of the link state; and a link controlunit for controlling the link transfer of the data in consideration ofthe determined level of the link state.
 12. The module as claimed inclaim 11, wherein the link level determination unit stores the number oftimes of attempted data transfer equivalent to a predefined level of thelink state, and the link control unit controls the number of times ofattempted data transfer by applying the determined level of the linkstate to the predefined level of the link state.
 13. The module asclaimed in claim 11, wherein the link level determination unit stores alength of a waiting time interval for data transfer equivalent to apredefined level of the link state, and the link control unit controls alength of a waiting time interval for data transfer by applying thedetermined level of the link state according to the predefined level ofthe link state.
 14. The module as claimed in claim 11, wherein the linklevel determination unit stores the number of data frames to betransmitted by duplicating original data, depending on a predefinedlevel of the link state, and the link control unit controls the numberof data frames to be transmitted by duplicating original data with theapplication of the determined level of the link state to the predefinedlevel of the link state.
 15. The module as claimed in claim 11, whereinthe link level determination unit and the link control unit are providedto a network layer.
 16. The module as claimed in claim 15, wherein thelink level determination unit checks a type of data received from anupper layer.
 17. The module as claimed in claim 15, wherein the linklevel determination unit receives an LQIV from a physical layer, andchecks a magnitude of the received LQIV.
 18. The module as claimed inclaim 17, wherein the link level determination unit is requested totransmit data by an upper layer, and requests the physical layer toprovide the LQIV in real-time.
 19. The module as claimed in claim 17,wherein the link level determination unit requests the LQIV in aninitialization process of a network, temporarily stores the LQIV, andchecks the stored LQIV as occasion demands.
 20. An apparatus fortransmitting/receiving data, having a physical layer, a Medium AccessControl (MAC) Layer, and a network layer in a Wireless Sensor Network(WSN), the apparatus comprising: a module for transmitting/receivingdata in the network layer thereof the module comprising: a link leveldetermination unit for predefining a level of a link state, depending oncharacteristics of data and a Link Quality Indication Value (LQIV) tostore a predefined level of the link state, and for determining a levelof a link state by applying characteristics of data and an LQIV receivedfrom the physical layer to the predefined level of the link state; and alink control unit for controlling the link transfer of the data inconsideration of the determined level of the link state.